Method and apparatus for multi-line intra prediction

ABSTRACT

A method of and an apparatus for controlling intra prediction for decoding of a video sequence are provided. The method includes, based on a reference line index signaling, to a decoder, a first reference line nearest to a coding unit, among a plurality of reference lines adjacent to the coding unit, applying intra smoothing on only the first reference line, based on the intra smoothing being applied only on the first reference line, applying intra prediction on the coding unit, and based on the intra prediction being applied on the coding unit, applying a position-dependent intra prediction combination (PDPC) on only the first reference line.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/199,891, filed on Nov. 26, 2018, in the United States Patent andTrademark Office, which claims priority from U.S. Provisional PatentApplication No. 62/724,575, filed on Aug. 29, 2018, in the United StatesPatent and Trademark Office, which are incorporated herein by referencein their entireties.

BACKGROUND 1. Field

Methods and apparatuses consistent with embodiments relate to videoprocessing, and more particularly, a method and an apparatus formulti-line intra prediction.

2. Description of Related Art

Intra prediction modes used in High Efficiency Video Coding (HEVC) areillustrated in FIG. 1. In HEVC, there is a total of 35 intra predictionmodes, among which mode 10 (101) is a horizontal mode, mode 26 (102) isa vertical mode, and mode 2 (103), mode 18 (104) and mode 34 (105) arediagonal modes. The intra prediction modes are signaled by three mostprobable modes (MPMs) and 32 remaining modes.

SUMMARY

According to embodiments, a method of controlling intra prediction fordecoding of a video sequence is performed by at least one processor andincludes, based on a reference line index signaling, to a decoder, afirst reference line nearest to a coding unit, among a plurality ofreference lines adjacent to the coding unit, applying intra smoothing ononly the first reference line, based on the intra smoothing beingapplied only on the first reference line, applying intra prediction onthe coding unit, and based on the intra prediction being applied on thecoding unit, applying a position-dependent intra prediction combination(PDPC) on only the first reference line.

According to embodiments, an apparatus for controlling intra predictionfor decoding of a video sequence includes at least one memory configuredto store computer program code, and at least one processor configured toaccess the at least one memory and operate according to the computerprogram code. The computer program code includes first applying codeconfigured to cause the at least one processor to, based on a referenceline index signaling, to a decoder, a first reference line nearest to acoding unit, among a plurality of reference lines adjacent to the codingunit, apply intra smoothing on only the first reference line, secondapplying code configured to cause the at least one processor to, basedon the intra smoothing being applied only on the first reference line,apply intra prediction on the coding unit, and third applying codeconfigured to cause the at least one processor to, based on the intraprediction being applied on the coding unit, apply a PDPC on only thefirst reference line.

According to embodiments, a non-transitory computer-readable storagemedium storing instructions that cause a processor to, based on areference line index signaling, to a decoder, a first reference linenearest to a coding unit, among a plurality of reference lines adjacentto the coding unit, apply intra smoothing on only the first referenceline, based on the intra smoothing being applied only on the firstreference line, apply intra prediction on the coding unit, and based onthe intra prediction being applied on the coding unit, apply a PDPC ononly the first reference line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of intra prediction modes in HEVC.

FIG. 2 is a simplified block diagram of a communication system accordingto an embodiment.

FIG. 3 is a diagram of a placement of a video encoder and a videodecoder in a streaming environment, according to an embodiment.

FIG. 4 is a functional block diagram of a video decoder according to anembodiment.

FIG. 5 is a functional block diagram of a video encoder according to anembodiment.

FIG. 6 is a diagram of intra prediction modes in Versatile Video Coding(VVC) Draft 2.

FIG. 7 is a diagram illustrating DC mode PDPC weights (wL, wT, wTL) for(0, 0) and (1, 0) positions inside one 4×4 block, in the VVC Draft 2.

FIG. 8 is a diagram of four reference lines adjacent to a coding blockunit, for intra prediction, according to an embodiment.

FIG. 9 is a flowchart illustrating a method of controlling intraprediction for decoding of a video sequence, according to an embodiment.

FIG. 10 is a simplified block diagram of an apparatus for controllingintra prediction for decoding of a video sequence, according to anembodiment.

FIG. 11 is a diagram of a computer system suitable for implementingembodiments.

DETAILED DESCRIPTION

FIG. 2 is a simplified block diagram of a communication system (200)according to an embodiment. The communication system (200) may includeat least two terminals (210-220) interconnected via a network (250). Forunidirectional transmission of data, a first terminal (210) may codevideo data at a local location for transmission to the other terminal(220) via the network (250). The second terminal (220) may receive thecoded video data of the other terminal from the network (250), decodethe coded data and display the recovered video data. Unidirectional datatransmission may be common in media serving applications and the like.

FIG. 2 illustrates a second pair of terminals (230, 240) provided tosupport bidirectional transmission of coded video that may occur, forexample, during videoconferencing. For bidirectional transmission ofdata, each terminal (230, 240) may code video data captured at a locallocation for transmission to the other terminal via the network (250).Each terminal (230, 240) also may receive the coded video datatransmitted by the other terminal, may decode the coded data and maydisplay the recovered video data at a local display device.

In FIG. 2, the terminals (210-240) may be illustrated as servers,personal computers and smart phones but the principles of embodimentsare not so limited. Embodiments find application with laptop computers,tablet computers, media players and/or dedicated video conferencingequipment. The network (250) represents any number of networks thatconvey coded video data among the terminals (210-240), including forexample wireline and/or wireless communication networks. Thecommunication network (250) may exchange data in circuit-switched and/orpacket-switched channels. Representative networks includetelecommunications networks, local area networks, wide area networksand/or the Internet. For the purposes of the present discussion, thearchitecture and topology of the network (250) may be immaterial to theoperation of embodiments unless explained herein below.

FIG. 3 is a diagram of a placement of a video encoder and a videodecoder in a streaming environment, according to an embodiment. Thedisclosed subject matter can be equally applicable to other videoenabled applications, including, for example, video conferencing,digital TV, storing of compressed video on digital media including CD,DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313) that caninclude a video source (301), for example a digital camera, creating,for example, an uncompressed video sample stream (302). That samplestream (302), depicted as a bold line to emphasize a high data volumewhen compared to encoded video bitstreams, can be processed by anencoder (303) coupled to the camera (301). The encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video bitstream (304), depicted as a thin line toemphasize the lower data volume when compared to the sample stream, canbe stored on a streaming server (305) for future use. One or morestreaming clients (306, 308) can access the streaming server (305) toretrieve copies (307, 309) of the encoded video bitstream (304). Aclient (306) can include a video decoder (310) which decodes theincoming copy of the encoded video bitstream (307) and creates anoutgoing video sample stream (311) that can be rendered on a display(312) or other rendering device (not depicted). In some streamingsystems, the video bitstreams (304, 307, 309) can be encoded accordingto certain video coding/compression standards. Examples of thosestandards include ITU-T Recommendation H.265. Under development is avideo coding standard informally known as VVC. The disclosed subjectmatter may be used in the context of VVC.

FIG. 4 is a functional block diagram of a video decoder (310) accordingto an embodiment.

A receiver (410) may receive one or more codec video sequences to bedecoded by the decoder (310); in the same or an embodiment, one codedvideo sequence at a time, where the decoding of each coded videosequence is independent from other coded video sequences. The codedvideo sequence may be received from a channel (412), which may be ahardware/software link to a storage device which stores the encodedvideo data. The receiver (410) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (410) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween receiver (410) and entropy decoder/parser (420) (“parser”henceforth). When receiver (410) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosychronous network, the buffer (415) may not be needed, or can besmall. For use on best effort packet networks such as the Internet, thebuffer (415) may be required, can be comparatively large and canadvantageously of adaptive size.

The video decoder (310) may include a parser (420) to reconstructsymbols (421) from the entropy coded video sequence. Categories of thosesymbols include information used to manage operation of the decoder(310), and potentially information to control a rendering device such asa display (312) that is not an integral part of the decoder but can becoupled to it, as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplementary EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence received. The coding ofthe coded video sequence can be in accordance with a video codingtechnology or standard, and can follow principles well known to a personskilled in the art, including variable length coding, Huffman coding,arithmetic coding with or without context sensitivity, and so forth. Theparser (420) may extract from the coded video sequence, a set ofsubgroup parameters for at least one of the subgroups of pixels in thevideo decoder, based upon at least one parameters corresponding to thegroup. Subgroups can include Groups of Pictures (GOPs), pictures, tiles,slices, macroblocks, Coding Units (CUs), blocks, Transform Units (TUs),Prediction Units (PUs) and so forth. The entropy decoder/parser may alsoextract from the coded video sequence information such as transformcoefficients, quantizer parameter (QP) values, motion vectors, and soforth.

The parser (420) may perform entropy decoding/parsing operation on thevideo sequence received from the buffer (415), so to create symbols(421). The parser (420) may receive encoded data, and selectively decodeparticular symbols (421). Further, the parser (420) may determinewhether the particular symbols (421) are to be provided to a MotionCompensation Prediction unit (453), a scaler/inverse transform unit(451), an Intra Prediction unit (452), or a loop filter unit (454).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, decoder (310) can beconceptually subdivided into a number of functional units as describedbelow. In a practical implementation operating under commercialconstraints, many of these units interact closely with each other andcan, at least partly, be integrated into each other. However, for thepurpose of describing the disclosed subject matter, the conceptualsubdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). It can output blockscomprising sample values that can be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current (partly reconstructed) picture(456). The aggregator (455), in some cases, adds, on a per sample basis,the prediction information the intra prediction unit (452) has generatedto the output sample information as provided by the scaler/inversetransform unit (451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a Motion Compensation Prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (in this case called the residual samples or residualsignal) so to generate output sample information. The addresses withinthe reference picture memory form where the motion compensation unitfetches prediction samples can be controlled by motion vectors,available to the motion compensation unit in the form of symbols (421)that can have, for example X, Y, and reference picture components.Motion compensation also can include interpolation of sample values asfetched from the reference picture memory when sub-sample exact motionvectors are in use, motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (454). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video bitstream andmade available to the loop filter unit (454) as symbols (421) from theparser (420), but can also be responsive to meta-information obtainedduring the decoding of previous (in decoding order) parts of the codedpicture or coded video sequence, as well as responsive to previouslyreconstructed and loop-filtered sample values.

The output of the loop filter unit (454) can be a sample stream that canbe output to the render device (312) as well as stored in the referencepicture memory (456) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. Once a coded picture is fullyreconstructed and the coded picture has been identified as a referencepicture (by, for example, parser (420)), the current reference picture(456) can become part of the reference picture buffer (457), and a freshcurrent picture memory can be reallocated before commencing thereconstruction of the following coded picture.

The video decoder (310) may perform decoding operations according to apredetermined video compression technology that may be documented in astandard, such as ITU-T Rec. H.265. The coded video sequence may conformto a syntax specified by the video compression technology or standardbeing used, in the sense that it adheres to the syntax of the videocompression technology or standard, as specified in the videocompression technology document or standard and specifically in theprofiles document therein. Also necessary for compliance can be that thecomplexity of the coded video sequence is within bounds as defined bythe level of the video compression technology or standard. In somecases, levels restrict the maximum picture size, maximum frame rate,maximum reconstruction sample rate (measured in, for example megasamplesper second), maximum reference picture size, and so on. Limits set bylevels can, in some cases, be further restricted through HypotheticalReference Decoder (HRD) specifications and metadata for HRD buffermanagement signaled in the coded video sequence.

In an embodiment, the receiver (410) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (310) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal-to-noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 is a functional block diagram of a video encoder (303) accordingto an embodiment.

The encoder (303) may receive video samples from a video source (301)(that is not part of the encoder) that may capture video image(s) to becoded by the encoder (303).

The video source (301) may provide the source video sequence to be codedby the encoder (303) in the form of a digital video sample stream thatcan be of any suitable bit depth (for example: 8 bit, 10 bit, 12 bit, .. . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ) and anysuitable sampling structure (for example Y CrCb 4:2:0, Y CrCb 4:4:4). Ina media serving system, the video source (301) may be a storage devicestoring previously prepared video. In a videoconferencing system, thevideo source (301) may be a camera that captures local image informationas a video sequence. Video data may be provided as a plurality ofindividual pictures that impart motion when viewed in sequence. Thepictures themselves may be organized as a spatial array of pixels,wherein each pixel can comprise one or more samples depending on thesampling structure, color space, etc. in use. A person skilled in theart can readily understand the relationship between pixels and samples.The description below focuses on samples.

According to an embodiment, the encoder (303) may code and compress thepictures of the source video sequence into a coded video sequence (543)in real time or under any other time constraints as required by theapplication. Enforcing appropriate coding speed is one function ofController (550). Controller controls other functional units asdescribed below and is functionally coupled to these units. The couplingis not depicted for clarity. Parameters set by controller can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. A person skilled in the art can readily identify other functionsof controller (550) as they may pertain to video encoder (303) optimizedfor a certain system design.

Some video encoders operate in what a person skilled in the art readilyrecognizes as a “coding loop.” As an oversimplified description, acoding loop can consist of the encoding part of an encoder (530)(“source coder” henceforth) (responsible for creating symbols based onan input picture to be coded, and a reference picture(s)), and a (local)decoder (533) embedded in the encoder (303) that reconstructs thesymbols to create the sample data that a (remote) decoder also wouldcreate (as any compression between symbols and coded video bitstream islossless in the video compression technologies considered in thedisclosed subject matter). That reconstructed sample stream is input tothe reference picture memory (534). As the decoding of a symbol streamleads to bit-exact results independent of decoder location (local orremote), the reference picture buffer content is also bit exact betweenlocal encoder and remote encoder. In other words, the prediction part ofan encoder “sees” as reference picture samples exactly the same samplevalues as a decoder would “see” when using prediction during decoding.This fundamental principle of reference picture synchronicity (andresulting drift, if synchronicity cannot be maintained, for examplebecause of channel errors) is well known to a person skilled in the art.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder (310), which has already been described in detail abovein conjunction with FIG. 4. Briefly referring also to FIG. 4, however,as symbols are available and en/decoding of symbols to a coded videosequence by entropy coder (545) and parser (420) can be lossless, theentropy decoding parts of decoder (310), including channel (412),receiver (410), buffer (415), and parser (420) may not be fullyimplemented in local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. The description of encodertechnologies can be abbreviated as they are the inverse of thecomprehensively described decoder technologies. Only in certain areas amore detail description is required and provided below.

As part of its operation, the source coder (530) may perform motioncompensated predictive coding, which codes an input frame predictivelywith reference to one or more previously-coded frames from the videosequence that were designated as “reference frames.” In this manner, thecoding engine (532) codes differences between pixel blocks of an inputframe and pixel blocks of reference frame(s) that may be selected asprediction reference(s) to the input frame.

The local video decoder (533) may decode coded video data of frames thatmay be designated as reference frames, based on symbols created by thesource coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 4), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on reference framesand may cause reconstructed reference frames to be stored in thereference picture cache (534). In this manner, the encoder (303) maystore copies of reconstructed reference frames locally that have commoncontent as the reconstructed reference frames that will be obtained by afar-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new frame to be coded, the predictor (535)may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the video coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder translatesthe symbols as generated by the various functional units into a codedvideo sequence, by loss-less compressing the symbols according totechnologies known to a person skilled in the art as, for exampleHuffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare it for transmission via acommunication channel (560), which may be a hardware/software link to astorage device that may store the encoded video data. The transmitter(540) may merge coded video data from the video coder (530) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the encoder (303). Duringcoding, the controller (550) may assign to each coded picture a certaincoded picture type, which may affect the coding techniques that may beapplied to the respective picture. For example, pictures often may beassigned as one of the following frame types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other frame in the sequence as a source of prediction.Some video codecs allow for different types of Intra pictures,including, for example Independent Decoder Refresh Pictures. A personskilled in the art is aware of those variants of I pictures and theirrespective applications and features.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded non-predictively,via spatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codednon-predictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video coder (303) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video coder (303) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The video coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

FIG. 6 is a diagram of intra prediction modes in VVC Draft 2.

In the VVC Draft 2, there is a total of 87 intra prediction modes asshown in FIG. 6, among which mode 18 (601) is a horizontal mode, mode 50(602) is a vertical mode, and mode 2 (603), mode 34 (604) and mode 66(605) are diagonal modes. Modes −1 to 10 and modes 67 to 76 are calledWide-Angle Intra Prediction (WAIP) modes.

A PDPC is applied to the following intra modes without signaling: aplanar mode, a DC mode, the WAIP modes, the horizontal mode, thevertical mode, a bottom-left angular mode (the mode 2 (603)) and its 8adjacent angular modes (modes 3 to 10), and a top-right angular mode(mode 66 (605)) and its 8 adjacent angular modes (modes 58 to 65).

A prediction sample pred(x,y) located at position (x, y) is predictedusing an intra prediction mode (DC, planar, angular) and a linearcombination of reference samples, according to the following PDPCexpression:pred(x,y)=(wL×R _(−1,y) +wT×R _(x,−1) −wTL×R_(−1,−1)+(64−wL−wT+wTL)×pred(x,y)+32)>>6,  (Equation 1)

where R_(x,−1), R_(−1,y), represent reference samples located at the top(T) and the left (L) of a current sample (x, y), respectively, andR−1,−1 represents a reference sample located at a top-left (TL) cornerof the current block.

For the DC mode, weights (wL, wT, WTL) are calculated as follows for ablock with dimensions of a width and a height:wT=32>>((y<<1)>>shift),wL=32>>((x<<1)>>shift),wTL=(wL>>4)+(wT>>4),  (Equation2)

with shift=(log 2(width)−2+log 2(height)−2+2)>>2.

For the planar mode, wTL=0, for the horizontal mode, wTL=wT, and for thevertical mode, wTL=wL. The PDPC weights can be calculated with adds andshifts only. A value of pred(x,y) can be computed in a single step usingEquation 1.

FIG. 7 is a diagram illustrating DC mode PDPC weights (wL, wT, wTL) for(0, 0) and (1, 0) positions inside one 4×4 block, in the VVC Draft 2.

Referring to FIG. 7, portion (a) illustrates DC mode PDPC weights (wL,wT, wTL) for a (0, 0) position inside one 4×4 block. Portion (b)illustrates DC mode PDPC weights (wL, wT, wTL) for a (1, 0) positioninside one 4×4 block.

If the PDPC is applied to the DC, planar, horizontal, and verticalmodes, additional boundary filters are not needed, such as an HEVC DCmode boundary filter or horizontal/vertical mode edge filters.

Portion (a) of FIG. 7 illustrates the definition of reference samplesRx,−1, R−1,y and R−1,−1 for the PDPC applied to the top-right angular ordiagonal mode. A prediction sample pred(x′, y′) is located at (x′, y′)within the prediction block. The coordinate x of the reference sampleRx,−1 is given by: x=x′+y′+1, and the coordinate y of the referencesample R−1,y is similarly given by: y=x′+y′+1.

The following clause from the VVC Draft 2 describes the PDPC:

8.2.4.2.9 Position-Dependent Intra Prediction Combination Process

Inputs to this process are:

-   -   the intra prediction mode predModeIntra,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height,    -   a variable refW specifying the reference samples width,    -   a variable refH specifying the reference samples height,    -   the predicted samples predSamples[x][y], with x=0 . . . nTbW−1        and y=0 . . . nTbH−1,    -   the neighbouring samples p[x][y], with x=1, y=1 . . . refH−1 and        x=0 . . . refW−1, y=1, a variable cIdx specifying the colour        component of the current block.        Outputs of this process are the modified predicted samples        predSamples[x][y] with x=0 . . . nTbW−1, y=0 . . . nTbH−1.        Depending on the value of cIdx, the function clip1Cmp is set as        follows:    -   If cIdx is equal to 0, clip1Cmp is set equal to Clip1_(Y).    -   Otherwise, clip1Cmp is set equal to Clip1_(C).        The variable nScale is set to ((Log 2(nTbW)+Log 2(nTbH)−2)>>2).        The reference sample arrays mainRef[x] and sideRef[y], with x=0        . . . refW and y=0 . . . refH are derived as follows:        mainRef[x]=p[x][−1]        sideRef[y]=p[−1][y]  (8-74)        The variables refL[x][y], refT[x][y], wT[y], wL[y] and wTL[x][y]        with x=0 . . . nTbW−1, y=0 . . . nTbH−1 are derived as follows:    -   If predModeIntra is equal to INTRA_PLANAR, INTRA_DC,        INTRA_ANGULAR18, or INTRA_ANGULAR50, the following applies:        refL[x][y]=p[−1][y]  (8-75)        refT[x][y]=p[x][−1]  (8-76)        wT[y]=32>>((y<<1)>>nScale)  (8-77)        wL[x]=32>>((x<<1)>>nScale)  (8-78)        wTL[x][y]=(predModeIntra==INTRA_DC)?((wL[x]>>4)+(wT[y]>>4)):0  (8-79)    -   Otherwise, if predModeIntra is equal to INTRA_ANGULAR2 or        INTRA_ANGULAR66, the following applies:        refL[x][y]=p[−1][x+y+1]  (8-80)        refT[x][y]=p[x+y+1][−1]  (8-81)        wT[y]=(32>>1)>>((y<<1)>>nScale)  (8-82)        wL[x]=(32>>1)>>((x<<1)>>nScale)  (8-83)        wTL[x][y]=0  (8-84)    -   Otherwise, if predModeIntra is less than or equal to        INTRA_ANGULAR10, the following ordered steps apply:        -   The variables dXPos[y], dXFrac[y], dXInt[y] and dX[y] are            derived as follows using invAngle as specified in clause            8.2.4.2.7 depending on intraPredMode:            dXPos[y]=((y+1)*invAngle+2)>>2            dXFrac[y]=dXPos[y]& 63            dX Int[y]=dXPos[y]>>6            dX[y]=x+dX Int[y]  (8-85)    -   The variables refL[x][y], refT[x][y], wT[y], wL[y] and wTL[x][y]        are derived as follows:        refL[x][y]=0  (8-86)        refT[x][y]=(dX[y]<refW−1)?((64−dXFrac[y])*mainRef[dX[y]]+dXFrac[y]*mainRef[dX[y]+1]+32)>>6:0  (8-87)        wT[y]=(dX[y]<refW−1)?32>>((y<<1)>>nScale):0  (8-88)        wL[x]=0  (8-89)        wTL[x][y]=0  (8-90)    -   Otherwise, if predModeIntra is greater than or equal to        INTRA_ANGULAR58, the following ordered steps apply:        -   The variables dYPos[x], dYFrac[x], dYInt[x] and dY[x] are            derived as follows using invAngle as specified in clause            8.2.4.2.7 depending on intraPredMode:            dYPos[x]=((x+1)*invAngle+2)>>2            dYFrac[x]=dYPos[x]& 63            dY Int[x]=dYPos[x]>>6            dY[x]=x+dYInt[x]  (8-91)        -   The variables refL[x][y], refT[x][y], wT[y], wL[y] and            wTL[x][y] are derived as follows:            refL[x][y]=(dY[x]<refH−1)?((64−dYFrac[x])*sideRef[dY[x]]+dYFrac[x]*sideRef[dY[x]+1]+32)>>6:0  (8-92)            refT[x][y]=0  (8-93)            wT[y]=0  (8-94)            wL[x]=(dY[x]<refH−1)?32>>((x<<1)>>nScale):0  (8-95)            wTL[x][y]=0  (8-96)    -   Otherwise, refL[x][y], refT[x][y], wT[y], wL[y] and wTL[x][y]        are all set equal to 0.        The values of the filtered samples filtSamples[x][y], with x=0 .        . . nTbW−1, y=0 . . . nTbH−1 are derived as follows:        filtSamples[x][y]=clip1Cmp((refL[x][y]*wL+refT[x][y]*wT−p[−1][−1]*wTL[x][y]+(64−wL[x]−wT[y]+wTL[x][y])*predSamples[x][y]+32)>>6)  (8-97)

In the VVC Draft 2, for a luma component, neighboring samples used forintra prediction sample generations are filtered before a generationprocess, namely an intra smoothing process. The filtering is controlledby a given intra prediction mode and a transform block size. If theintra prediction mode is a DC mode or the transform block size is equalto 4×4, neighboring samples are not filtered. If a distance between thegiven intra prediction mode and a vertical mode (or a horizontal mode)is larger than a predefined threshold, the filtering process is enabled.For neighboring sample filtering, a [1, 2, 1] filter and a bi-linearfilter are used.

The following clause from VVC Draft 2 describes the intra smoothingprocess:

8.2.4.2.4 Reference Sample Filtering Process

Inputs to this process are:

-   -   the (unfiltered) neighbouring samples refUnfilt[x][y], with x=1,        y=1 . . . refH−1 and x=0 . . . refW−1, y=1,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height,    -   a variable refW specifying the reference samples width,    -   a variable refH specifying the reference samples height,    -   a variable cIdx specifying the colour component of the current        block.        Outputs of this process are the reference samples p[x][y], with        x=1, y=1 . . . refH−1 and x=0 . . . refW−1, y=−1.        The variable nTbS is set equal to (Log 2 (nTbW)+Log 2        (nTbH))>>1.        The variable whRatio is set equal to min(abs(Log 2(nTbW/nTbH)),        2).        The variable wideAngle is derived as follows:    -   If all of the following conditions are true, wideAngle is set        equal to 1.        -   nTbW is greater than nTbH        -   predModeIntra is greater than or equal to 2        -   predModeIntra is less than (whRatio>1) ? 12:8    -   Otherwise, if all of the following conditions are true,        wideAngle is set equal to 1.        -   nTbH is greater than nTbW        -   predModeIntra is less than or equal to 66        -   predModeIntra is greater than (whRatio>1) ? 56:60    -   Otherwise, wideAngle is set to 0.        The variable filterFlag is derived as follows:    -   If one or more of the following conditions is true, filterFlag        is set equal to 0:        -   predModeIntra is equal to INTRA_DC,        -   cIdx is not equal to 0.    -   Otherwise, the following applies:        -   The variable minDistVerHor is set equal to            Min(Abs(predModeIntra−50), Abs(predModeIntra−18)).        -   The variable intraHorVerDistThres[nTbS] is specified in            Table 8-4.        -   The variable filterFlag is derived as follows:            -   If minDistVerHor is greater than                intraHorVerDistThres[nTbS] or wideAngle is equal to 1,                filterFlag is set equal to 1.            -   Otherwise, filterFlag is set equal to 0.

TABLE 8-4 Specification of intraHorVerDistThres[nTbS] for varioustransform block sizes nTbS = 2 nTbS = 3 nTbS = 4 nTbS = 5 nTbS = 6 nTbS= 7 intraHorVerDistThres[nTbS] 20 14 2 0 20 0For the derivation of the reference samples p[x][y] the followingapplies:

-   -   If filterFlag is equal to 1, the filtered sample values p[x][y]        with x=−1, y=−1 . . . refH−1 and x=0 . . . refW−1, y=−1 are        derived as follows:        p[−1][−1]=(refUnfilt[−1][0]+2*refUnfilt[−1][−1]+refUnfilt[0][−1]+2)>>2  (8-20)        p[−1][y]=(refUnfilt[−1][y+1]+2*refUnfilt[−1][y]+refUnfilt[−1][y−1]+2)>>2        for y=0 . . . refH−2  (8-21)        p[−1][refH−1]=refUnfilt[−1][refH−1]  (8-22)        pF[x][−1]=(refUnfilt[x−1][−1]+2*refUnfilt[x][−1]+refUnfilt[x+1][−1]+2)>>2        for x=0 . . . refW−2  (8-23)        p[refW−1][−1]=refUnfilt[refW−1][−1]  (8-24)    -   Otherwise, the reference samples values p[x][y] are set equal to        the unfiltered sample values refUnfilt[x][y] with x=−1, y=−1 . .        . refH−1 and x=0 . . . refW−1, y=−1.

In the VVC Draft 2, multi-line intra prediction uses more referencelines for intra prediction, and an encoder decides and signals whichreference line is used to generate an intra predictor. A reference lineindex is signaled before intra prediction modes, and planar and DC modesare excluded from the intra prediction modes in when a nonzero referenceline index is signaled.

FIG. 8 is a diagram of four reference lines (881 to 884) adjacent to acoding block unit (810), for intra prediction, according to anembodiment.

Referring to FIG. 8, an example of 4 reference lines (881 to 884) isdepicted, and each of the reference lines (881 to 884) is composed ofsix segments A to F (820 to 870). A top-left reference sample (880) tothe top-left of the block unit (810) is also depicted in black. Inaddition, segments A and F (820 to 870) are padded with the closestsamples (890) from segments B and E (830 and 860), respectively.

Referring again to FIG. 6, wide angles beyond a range of predictiondirections covered by conventional intra prediction modes are indicatedby dotted arrows, and respectively correspond to wide angular intraprediction modes. These wide angles may be applied for non-square blocksas follows:

Angles going beyond 45 degrees in a top-right direction (intraprediction mode 34 in HEVC) if a block width is larger than a blockheight.

Angles going beyond 45 degrees in a bottom-left direction (intraprediction mode 2 in HEVC) if the block height is larger than the blockwidth.

The replaced modes are signaled using an original method and remapped toindices of the wide angular intra prediction modes after parsing. Atotal number of the intra prediction modes is unchanged, i.e., 35, andan intra mode coding is unchanged.

Currently, PDPC is applied to all reference lines. However, a PDPCprocess will make generated prediction samples similar by usingdifferent reference lines, which is not a desirable design.

Currently, intra smoothing is applied to all reference lines. However,an intra smoothing process will make reference samples in differentlines much more closer, which is not a desirable design.

To address these problems, embodiments are discussed below, which may beused separately or combined in any order. In the following description,a line index of a nearest reference line is 0 (i.e., the reference line881 of FIG. 8). A maximum signaled reference line number is denoted asN. Further, the term “PDPC” may refer to a simplified PDPC as describedin the VVC Draft 2, clause 8.2.4.2.9.

In embodiments, the PDPC is applied on only the nearest reference line.

In embodiments, intra smoothing process is applied on only the nearestreference line.

In embodiments, the intra smoothing process is applied on only certainreference lines (i.e., 881 to 884 of FIG. 8). In an embodiment, theintra smoothing process is only applied to reference line 0 (i.e., 881of FIG. 8) and 1 (i.e., 882 of FIG. 8). In another embodiment, the intrasmoothing process is applied to reference lines 0 and 3 (i.e., 884 ofFIG. 8). In still another embodiment, the intra smoothing process isapplied to reference lines 0 and 2 (i.e., 883 of FIG. 8). In yet anotherembodiment, the intra smoothing process is not applied to one referenceline, and the intra smoothing process is applied to all other referencelines. For example, the intra smoothing process is not applied toreference line 3.

In embodiments, the PDPC is applied on only certain selected referencelines. In an embodiment, the PDPC is only applied to reference lines 0and 1. In another embodiment, the PDPC is applied to reference lines 0and 3. In still another embodiment, the PDPC is applied to referencelines 0 and 2. In yet another embodiment, the PDPC is not applied to onereference line, and PDPC is applied to all other reference lines. Forexample, the PDPC is not applied to reference line 3.

In embodiments, the PDPC is applied on only non-zero reference lines(i.e., 882 to 884 of FIG. 8), but when it is applied to the non-zeroreference lines, the PDPC is only applied to certain intra predictionmodes. The following embodiments can be applied separately or combinedin any order. In an embodiment, when a non-zero reference line is used,the PDPC is only applied to a planar mode and/or a DC mode. In anotherembodiment, when the non-zero reference line is used, the PDPC is onlyapplied to horizontal and vertical modes. In still another embodiment,when the non-zero reference line is used, the PDPC is only applied to adiagonal mode (mode 2 or 66 as shown in FIG. 6). In yet anotherembodiment, when the non-zero reference line is used, the PDPC is onlyapplied to intra prediction modes close to mode 2 and mode 66, forexample, modes 3 to 10 and modes 58 to 65 as shown in FIG. 6. In yetanother embodiment, when the non-zero reference line is used, the PDPCis only applied to WAIP modes.

In embodiments, different combinations of the PDPC and the intrasmoothing process are used for different reference lines. In anembodiment, the PDPC and the intra smoothing is applied to referenceline 0, only the PDPC is applied to reference line 1, only the intrasmoothing is applied to reference line 2, and neither the PDPC nor theintra smoothing is applied to reference line 3. In another embodiment,if N is equal to 4, both the PDPC and the intra smoothing are applied toreference line 0, and/or there is at least one reference line for whicheither only the PDPC or the intra smoothing is applied, but not both,and/or there is at least one reference line for which neither the PDPCnor the intra smoothing is applied. In still another embodiment, if N isequal to 3, both the PDPC and the intra smoothing are applied toreference line 0, only the PDPC is applied to one of the non-zeroreference lines, and neither the PDPC nor the intra smoothing is appliedto one of the reference lines. In yet another embodiment, if N is equalto 3, both the PDPC and the intra smoothing is applied to reference line0, only the intra smoothing is applied to at least one of the non-zeroreference lines, neither the PDPC nor the intra smoothing is applied toat least one of the reference lines.

In embodiments, the planar and DC modes are also used for a non-zeroreference line, but the PDPC and the intra smoothing for planar and DCmodes in different reference lines are different. In an embodiment, thePDPC and the intra smoothing are applied to planar and DC modes in thenearest reference line, and the PDPC and the intra smoothing are notapplied to the planar and DC modes in other reference lines. In anotherembodiment, the PDPC and the intra smoothing are applied to the planarand DC modes in the nearest reference line, either one or none of thePDPC and the intra smoothing is applied to the planar and DC modes inthe non-zero reference lines.

In embodiments, the PDPC is not applied to wide angles for the non-zeroreference lines.

In embodiments, the intra smoothing is not applied to wide angles forthe non-zero reference lines.

In embodiments, the intra smoothing is reference line dependent. Thatis, the intra smoothing is applied for different intra prediction modesfor different reference lines. Threshold values controlling which intraprediction modes close to horizontal/vertical modes are excluded fromthe intra smoothing are dependent on a reference line index. In anembodiment, intra prediction modes applying the intra smoothing for acertain reference line index are fully covered by intra prediction modesapplying the intra smoothing for a smaller reference line index value,wherein the smaller reference line index value refers to a referenceline closer to a current block to be predicted.

In embodiments, the intra prediction modes that used the PDPC aredifferent for different reference lines. In an embodiment, the PDPC isapplied to a vertical direction and a horizontal direction in referenceline 0. However, in the non-zero reference lines, the PDPC is notapplied to the vertical and horizontal directions.

The following text describes the text changes (using underlines andstrikethroughs) using embodiments of disabling intra smoothing for anon-zero reference line, based on the VVC Draft 2.

8.2.4.2.1 General Intra Sample Prediction

Inputs to this process are:

-   -   a sample location (xTbCmp, yTbCmp) specifying the top-left        sample of the current transform block relative to the top-left        sample of the current picture,    -   a variable predModeIntra specifying the intra prediction mode,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height,    -   a variable refLine specifying the reference line index,    -   a variable cIdx specifying the colour component of the current        block.        Outputs of this process are the predicted samples        predSamples[x][y], with x=0 . . . nTbW−1, y=0 . . . nTbH−1.        The variable whRatio is set equal to min(abs(Log 2(nTbW/nTbH)),        2).        The variables refW and refH are derived as follows:        refW=(nTbH>nTbW)?(nTbW+(nTbH>>whRatio)+Ceil(nTbH/32)):(nTbW*2)  (8-15)        refH=(nTbW>nTbH)?(nTbH+(nTbW>>whRatio)+Ceil(nTbW/32)):(nTbH*2)  (8-16)        For the generation of the reference samples p[x][y] with x=−1,        y=−1 . . . refH−1 and x=0 . . . refW−1, y=−1, the following        ordered steps apply:    -   1. The reference sample availability marking process as        specified in clause 8.2.4.2.2 is invoked with the sample        location (xTbCmp, yTbCmp), the reference sample width refW, the        reference sample height refH, the colour component index cIdx as        inputs, and the reference samples refUnfilt[x][y] with x=−1,        y=−1 refH−1 and x=0 . . . refW−1, y=−1 as output.    -   2. When at least one sample refUnfilt[x][y] with x=−1, y=−1 . .        . refH−1 and x=0 . . . refW−1, y=−1 is marked as “not available        for intra prediction”, the reference sample substitution process        as specified in clause 8.2.4.2.3 is invoked with the reference        sample width refW, the reference sample height refH, the        reference samples refUnfilt[x][y] with x=−1, y=−1 . . . refH−1        and x=0 . . . refW−1, y=−1, and the colour component index cIdx        as inputs, and the modified reference samples refUnfilt[x][y]        with x=−1, y=−1 . . . refH−1 and x=0 . . . refW−1, y=−1 as        output.    -   3. The reference sample filtering process as specified in clause        8.2.4.2.4 is invoked with the unfiltered samples refUnfilt[x][y]        with x=−1, y=−1 . . . refH−1 and x=0 . . . refW−1, y=−1, the        transform block width nTbW and height nTbH, the reference sample        width refW, the reference sample height refH, the reference line        index refLine, and the colour component index cIdx as inputs,        and the reference samples p[x][y] with x=−1, y=−1 . . . refH−1        and x=0 . . . refW−1, y=−1 as output.        The intra sample prediction process according to predModeIntra        applies as follows:    -   If predModeIntra is equal to INTRA_PLANAR, the corresponding        intra prediction mode process specified in clause 8.2.4.2.5 is        invoked with the reference sample array p, the transform block        width nTbW, and the transform block height nTbH as inputs, and        the output is the predicted sample array predSamples.    -   Otherwise, if predModeIntra is equal to INTRA_DC, the        corresponding intra prediction mode process specified in clause        8.2.4.2.6 is invoked with the transform block width nTbW, the        transform block height nTbH, and the reference sample array p as        inputs, and the output is the predicted sample array        predSamples.    -   Otherwise if predModeIntra is equal to INTRA_CCLM, the        corresponding intra prediction mode process specified in clause        8.2.4.2.8 is invoked with the sample location (xTbC, yTbC) set        equal to (xTbCmp, yTbCmp), the prediction block width nTbW and        height nTbH, and the reference sample array p as inputs, and the        output is the predicted sample array predSamples.    -   Otherwise, the corresponding intra prediction mode process        specified in clause 8.2.4.2.7 is invoked with the intra        prediction mode predModeIntra, the transform block width nTbW,        the transform block height nTbH, the reference sample width        refW, the reference sample height refH, and the reference sample        array p as inputs, and the modified intra prediction mode        predModeIntra and the predicted sample array predSamples as        outputs.        When one of the following conditions is true, the        position-dependent prediction combination process specified in        clause 8.2.4.2.9 is invoked with the intra prediction mode        predModeIntra, the transform block width nTbW, the transform        block height nTbH, the predicted samples predSamples[x][y], with        x=0 . . . nTbW−1, y=0 . . . nTbH−1, the reference sample width        refW, the reference sample height refH, the reference samples        p[x][y], with x=−1, y=−1 . . . refH−1 and x=0 . . . refW−1,        y=−1, and the colour component index cIdx as inputs, and the        output is the modified predicted sample array predSamples:    -   predModeIntra is equal to INTRA_PLANAR    -   predModeIntra is equal to INTRA_DC    -   predModeIntra is equal to INTRA_ANGULAR18    -   predModeIntra is equal to INTRA_ANGULAR50    -   predModeIntra is less than or equal to INTRA_ANGULAR10    -   predModeIntra is greater than or equal to INTRA_ANGULAR58        8.2.4.2.4 Reference Sample Filtering Process        Inputs to this process are:    -   the (unfiltered) neighbouring samples refUnfilt[x][y], with        x=−1, y=−1 . . . refH−1 and x=0 . . . refW−1, y=−1,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height,    -   a variable refW specifying the reference samples width,    -   a variable refH specifying the reference samples height,    -   a variable refLine specifying the reference line index,    -   a variable cIdx specifying the colour component of the current        block.        Outputs of this process are the reference samples p[x][y], with        x=−1, y=−1 . . . refH−1 and x=0 . . . refW−1, y=−1.        The variable nTbS is set equal to (Log 2 (nTbW)+Log 2        (nTbH))>>1.        The variable whRatio is set equal to min(abs(Log 2(nTbW/nTbH)),        2).        The variable wideAngle is derived as follows:    -   If all of the following conditions are true, wideAngle is set        equal to 1.        -   nTbW is greater than nTbH        -   predModeIntra is greater than or equal to 2        -   predModeIntra is less than (whRatio>1) ? 12:8    -   Otherwise, if all of the following conditions are true,        wideAngle is set equal to 1.        -   nTbH is greater than nTbW        -   predModeIntra is less than or equal to 66        -   predModeIntra is greater than (whRatio>1) ? 56:60    -   Otherwise, wideAngle is set to 0.        The variable filterFlag is derived as follows:    -   If one or more of the following conditions is true, filterFlag        is set equal to 0:        -   predModeIntra is equal to INTRA_DC,        -   cIdx is not equal to 0.        -   refLine is not equal to 0.    -   Otherwise, the following applies:        -   The variable minDistVerHor is set equal to            Min(Abs(predModeIntra−50), Abs(predModeIntra−18)).        -   The variable intraHorVerDistThres[nTbS] is specified in            Table 8-4.        -   The variable filterFlag is derived as follows:            -   If minDistVerHor is greater than                intraHorVerDistThres[nTbS] or wideAngle is equal to 1,                filterFlag is set equal to 1.            -   Otherwise, filterFlag is set equal to 0.

TABLE 8-4 Specification of intraHorVerDistThres[nTbS] for varioustransform block sizes nTbS = 2 nTbS = 3 nTbS = 4 nTbS = 5 nTbS = 6 nTbS= 7 intraHorVerDistThres[nTbS] 20 14 2 0 20 0For the derivation of the reference samples p[x][y] the followingapplies:

-   -   If filterFlag is equal to 1, the filtered sample values p[x][y]        with x=−1,y=−1 . . . refH−1 and x=0 . . . refW−1, y=−1 are        derived as follows:        p[−1][−1]=(refUnfilt[−1][0]+2*refUnfilt[−1][−1]+refUnfilt[0][−1]+2)>>2  (8-20)        p[−1][y]=(refUnfilt[−1][y+1]+2*refUnfilt[−1][y]+refUnfilt[−1][y−1]+2)>>2        for y=0 . . . refH−2  (8-21)        p[−1][refH−1]=refUnfilt[−1][refH−1]  (8-22)        pF[x][−1]=(refUnfilt[x−1][−1]+2*refUnfilt[x][−1]+refUnfilt[x+1][−1]+2)>>2        for x=0 . . . refW−2  (8-23)        p[refW−1][−1]=refUnfilt[refW−1][−1]  (8-24)        Otherwise, the reference samples values p[x][y] are set equal to        the unfiltered sample values refUnfilt[x][y] with x=−1, y=−1 . .        . refH−1 and x=0 . . . refW−1, y=−1.

The following text describes the text changes (using underlines andstrikethroughs) using embodiments of disabling PDPC for a non-zeroreference line, based on the latest version of the VVC Draft 2.

8.2.4.2.1 General Intra Sample Prediction

Inputs to this process are:

-   -   a sample location (xTbCmp, yTbCmp) specifying the top-left        sample of the current transform block relative to the top-left        sample of the current picture,    -   a variable predModeIntra specifying the intra prediction mode,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height,    -   a variable refLine specifying the reference line index,    -   a variable cIdx specifying the colour component of the current        block.        Outputs of this process are the predicted samples        predSamples[x][y], with x=0 . . . nTbW−1, y=0 . . . nTbH−1.        The variable whRatio is set equal to min(abs(Log 2(nTbW/nTbH)),        2).        The variables refW and refH are derived as follows:        refW=(nTbH>nTbW)?(nTbW+(nTbH>>whRatio)+Ceil(nTbH/32)):(nTbW*2)  (8-15)        refH=(nTbW>nTbH)?(nTbH+(nTbW>>whRatio)+Ceil(nTbW/32)):(nTbH*2)  (8-16)        For the generation of the reference samples p[x][y] with x=−1,        y=−1 . . . refH−1 and x=0 . . . refW−1, y=−1, the following        ordered steps apply:    -   4. The reference sample availability marking process as        specified in clause 8.2.4.2.2 is invoked with the sample        location (xTbCmp, yTbCmp), the reference sample width refW, the        reference sample height refH, the colour component index cIdx as        inputs, and the reference samples refUnfilt[x][y] with x=−1,        y=−1 refH−1 and x=0 . . . refW−1, y=−1 as output.    -   5. When at least one sample refUnfilt[x][y] with x=−1, y=−1 . .        . refH−1 and x=0 . . . refW−1, y=−1 is marked as “not available        for intra prediction”, the reference sample substitution process        as specified in clause 8.2.4.2.3 is invoked with the reference        sample width refW, the reference sample height refH, the        reference samples refUnfilt[x][y] with x=−1, y=−1 . . . refH−1        and x=0 . . . refW−1, y=−1, and the colour component index cIdx        as inputs, and the modified reference samples refUnfilt[x][y]        with x=−1, y=−1 . . . refH−1 and x=0 . . . refW−1, y=−1 as        output.    -   6. The reference sample filtering process as specified in clause        8.2.4.2.4 is invoked with the unfiltered samples refUnfilt[x][y]        with x=−1, y=−1 . . . refH−1 and x=0 . . . refW−1, y=−1, the        transform block width nTbW and height nTbH, the reference sample        width refW, the reference sample height refH, and the colour        component index cIdx as inputs, and the reference samples        p[x][y] with x=−1, y=−1 . . . refH−1 and x=0 . . . refW−1, y=−1        as output.        The intra sample prediction process according to predModeIntra        applies as follows:    -   If predModeIntra is equal to INTRA_PLANAR, the corresponding        intra prediction mode process specified in clause 8.2.4.2.5 is        invoked with the reference sample array p, the transform block        width nTbW, and the transform block height nTbH as inputs, and        the output is the predicted sample array predSamples.    -   Otherwise, if predModeIntra is equal to INTRA_DC, the        corresponding intra prediction mode process specified in clause        8.2.4.2.6 is invoked with the transform block width nTbW, the        transform block height nTbH, and the reference sample array p as        inputs, and the output is the predicted sample array        predSamples.    -   Otherwise if predModeIntra is equal to INTRA_CCLM, the        corresponding intra prediction mode process specified in clause        8.2.4.2.8 is invoked with the sample location (xTbC, yTbC) set        equal to (xTbCmp, yTbCmp), the prediction block width nTbW and        height nTbH, and the reference sample array p as inputs, and the        output is the predicted sample array predSamples.    -   Otherwise, the corresponding intra prediction mode process        specified in clause 8.2.4.2.7 is invoked with the intra        prediction mode predModeIntra, the transform block width nTbW,        the transform block height nTbH, the reference sample width        refW, the reference sample height refH, and the reference sample        array p as inputs, and the modified intra prediction mode        predModeIntra and the predicted sample array predSamples as        outputs.        When one of the following conditions is true, the        position-dependent prediction combination process specified in        clause 8.2.4.2.9 is invoked with the intra prediction mode        predModeIntra, the transform block width nTbW, the transform        block height nTbH, the predicted samples predSamples[x][y], with        x=0 . . . nTbW−1, y=0 . . . nTbH−1, the reference sample width        refW, the reference sample height refH, the reference samples        p[x][y], with x=−1, y=−1 . . . refH−1 and x=0 . . . refW−1,        y=−1, and the colour component index cIdx as inputs, and the        output is the modified predicted sample array predSamples:    -   predModeIntra is equal to INTRA_PLANAR    -   predModeIntra is equal to INTRA_DC    -   predModeIntra is equal to INTRA_ANGULAR18    -   predModeIntra is equal to INTRA_ANGULAR50    -   predModeIntra is less than or equal to INTRA_ANGULAR10    -   predModeIntra is greater than or equal to INTRA_ANGULAR58        refLine is 0

FIG. 9 is a flowchart illustrating a method (900) of controlling intraprediction for decoding of a video sequence, according to an embodiment.In some implementations, one or more process blocks of FIG. 9 may beperformed by the decoder (310). In some implementations, one or moreprocess blocks of FIG. 9 may be performed by another device or a groupof devices separate from or including the decoder (310), such as theencoder (303).

Referring to FIG. 9, in a first block (910), the method (900) includesbased on a reference line index signaling, to a decoder, a firstreference line nearest to a coding unit, among a plurality of referencelines adjacent to the coding unit, applying intra smoothing on only thefirst reference line.

In a second block (920), the method (900) includes, based on the intrasmoothing being applied only on the first reference line, applying intraprediction on the coding unit.

In a third block (930), the method (900) includes, based on the intraprediction being applied on the coding unit, applying a PDPC on only thefirst reference line.

The method (900) may further include applying the intra smoothing on asecond reference line among the plurality of reference lines.

The method (900) may further include applying the intra smoothing onother reference lines among the plurality of reference lines, except fora single reference line among the plurality of reference lines.

The method (900) may further include, based on the intra predictionbeing applied on the coding unit, applying the PDPC on a secondreference line among the plurality of reference lines.

The method (900) may further include, based on the intra predictionbeing applied on the coding unit, applying the PDPC on other referencelines among the plurality of reference lines, except for a singlereference line among the plurality of reference lines.

The method (900) may further include determining whether an intraprediction angle corresponding to an intra prediction mode for decodingthe video sequence is greater than a predetermined angle correspondingto a diagonal direction of the coding unit, and based on the intraprediction angle being determined to be greater than the predeterminedangle, preventing application of the intra smoothing on other referencelines among the plurality of reference lines.

The method (900) may further include determining whether an intraprediction angle corresponding to an intra prediction mode for decodingthe video sequence is greater than a predetermined angle correspondingto a diagonal direction of the coding unit, and based on the intraprediction angle being determined to be greater than the predeterminedangle, preventing application of the PDPC on other reference lines amongthe plurality of reference lines.

The method (900) may further include applying the intra smoothing on atleast one of other reference lines among the plurality of referencelines, based on an intra prediction mode for decoding the video sequenceand an index of the at least one of the other reference lines.

The method (900) may further include determining a threshold index rangecorresponding to a plurality of intra prediction modes adjacent to ahorizontal direction of the coding unit, based on an index of a secondreference line among the plurality of reference lines, determiningwhether a current index value of a current intra prediction mode fordecoding the video sequence is within the threshold index range, andbased on the current index value being determined to be in the thresholdindex range, preventing application of the intra smoothing on the secondreference line.

The method (900) may further include determining a threshold index rangecorresponding to a plurality of intra prediction modes adjacent to avertical direction of the coding unit, based on an index of a secondreference line among the plurality of reference lines, determiningwhether a current index value of a current intra prediction mode fordecoding the video sequence is within the threshold index range, andbased on the current index value being determined to be in the thresholdindex range, preventing application of the intra smoothing on the secondreference line.

Although FIG. 9 shows example blocks of the method (900), in someimplementations, the method (900) may include additional blocks, fewerblocks, different blocks, or differently arranged blocks than thosedepicted in FIG. 9. Additionally, or alternatively, two or more of theblocks of the method (900) may be performed in parallel.

Further, the proposed methods may be implemented by processing circuitry(e.g., one or more processors or one or more integrated circuits). In anexample, the one or more processors execute a program that is stored ina non-transitory computer-readable medium to perform one or more of theproposed methods.

FIG. 10 is a simplified block diagram of an apparatus (1000) forcontrolling intra prediction for decoding of a video sequence, accordingto an embodiment.

Referring to FIG. 10, the apparatus (1000) includes first applying code(1010), second applying code (1020), and third applying code (1030).

The first applying code (1010) is configured to based on a referenceline index signaling, to a decoder, a first reference line nearest to acoding unit, among a plurality of reference lines adjacent to the codingunit, apply intra smoothing on only the first reference line.

The second applying code (1020) is configured to, based on the intrasmoothing being applied only on the first reference line, apply intraprediction on the coding unit.

The selecting code (1030) is configured to, based on the intraprediction being applied on the coding unit, apply a PDPC on only thefirst reference line.

The first applying code (1010) may be further configured to apply theintra smoothing on a second reference line among the plurality ofreference lines.

The first applying code (1010) may be further configured to apply theintra smoothing on other reference lines among the plurality ofreference lines, except for a single reference line among the pluralityof reference lines.

The third applying code (1030) may be further configured to, based onthe intra prediction being applied on the coding unit, apply the PDPC ona second reference line among the plurality of reference lines.

The third applying code (1030) may be further configured to, based onthe intra prediction being applied on the coding unit, apply the PDPC onother reference lines among the plurality of reference lines, except fora single reference line among the plurality of reference lines.

The first applying code (1010) may be further configured to determinewhether an intra prediction angle corresponding to an intra predictionmode for decoding the video sequence is greater than a predeterminedangle corresponding to a diagonal direction of the coding unit, andbased on the intra prediction angle being determined to be greater thanthe predetermined angle, prevent application of the intra smoothing onother reference lines among the plurality of reference lines.

The third applying code (1030) may be further configured to determinewhether an intra prediction angle corresponding to an intra predictionmode for decoding the video sequence is greater than a predeterminedangle corresponding to a diagonal direction of the coding unit, andbased on the intra prediction angle being determined to be greater thanthe predetermined angle, prevent application of the PDPC on otherreference lines among the plurality of reference lines.

The first applying code (1010) may be further configured to apply theintra smoothing on at least one of other reference lines among theplurality of reference lines, based on an intra prediction mode fordecoding the video sequence and an index of the at least one of theother reference lines.

The first applying code (1010) may be further configured to determine athreshold index range corresponding to a plurality of intra predictionmodes adjacent to a horizontal direction of the coding unit, based on anindex of a second reference line among the plurality of reference lines,determine whether a current index value of a current intra predictionmode for decoding the video sequence is within the threshold indexrange, and based on the current index value being determined to be inthe threshold index range, prevent application of the intra smoothing onthe second reference line.

The first applying code (1010) may be further configured to determine athreshold index range corresponding to a plurality of intra predictionmodes adjacent to a vertical direction of the coding unit, based on anindex of a second reference line among the plurality of reference lines,determine whether a current index value of a current intra predictionmode for decoding the video sequence is within the threshold indexrange, and based on the current index value being determined to be inthe threshold index range, prevent application of the intra smoothing onthe second reference line.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media.

FIG. 11 is a diagram of a computer system (1100) suitable forimplementing embodiments.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by computer central processing units (CPUs),Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 11 for computer system (1100) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments. Neither should the configuration of components beinterpreted as having any dependency or requirement relating to any oneor combination of components illustrated in the exemplary embodiment ofa computer system (1100).

Computer system (1100) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1101), mouse (1102), trackpad (1103), touchscreen (1110), data-glove (1104), joystick (1105), microphone (1106),scanner (1107), camera (1108).

Computer system (1100) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1110), data-glove (1104), or joystick (1105), but therecan also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1109), headphones(not depicted)), visual output devices (such as screens (1110) toinclude cathode ray tube (CRT) screens, liquid-crystal display (LCD)screens, plasma screens, organic light-emitting diode (OLED) screens,each with or without touch-screen input capability, each with or withouttactile feedback capability-some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1100) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1120) with CD/DVD or the like media (1121), thumb-drive (1122),removable hard drive or solid state drive (1123), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1100) can also include interface(s) to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include global systems for mobile communications(GSM), third generation (3G), fourth generation (4G), fifth generation(5G), Long-Term Evolution (LTE), and the like, TV wireline or wirelesswide area digital networks to include cable TV, satellite TV, andterrestrial broadcast TV, vehicular and industrial to include CANBus,and so forth. Certain networks commonly require external networkinterface adapters that attached to certain general purpose data portsor peripheral buses (1149) (such as, for example universal serial bus(USB) ports of the computer system (1100); others are commonlyintegrated into the core of the computer system (1100) by attachment toa system bus as described below (for example Ethernet interface into aPC computer system or cellular network interface into a smartphonecomputer system). Using any of these networks, computer system (1100)can communicate with other entities. Such communication can beuni-directional, receive only (for example, broadcast TV),uni-directional send-only (for example CANbus to certain CANbusdevices), or bi-directional, for example to other computer systems usinglocal or wide area digital networks. Certain protocols and protocolstacks can be used on each of those networks and network interfaces asdescribed above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1140) of thecomputer system (1100).

The core (1140) can include one or more Central Processing Units (CPU)(1141), Graphics Processing Units (GPU) (1142), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1143), hardware accelerators (1144) for certain tasks, and so forth.These devices, along with Read-only memory (ROM) (1145), Random-accessmemory (RAM) (1146), internal mass storage such as internal non-useraccessible hard drives, solid-state drives (SSDs), and the like (1147),may be connected through a system bus (1148). In some computer systems,the system bus (1148) can be accessible in the form of one or morephysical plugs to enable extensions by additional CPUs, GPU, and thelike. The peripheral devices can be attached either directly to thecore's system bus (1148), or through a peripheral bus (1149).Architectures for a peripheral bus include peripheral componentinterconnect (PCI), USB, and the like.

CPUs (1141), GPUs (1142), FPGAs (1143), and accelerators (1144) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1145) or RAM (1146). Transitional data can also be stored in RAM(1146), whereas permanent data can be stored for example, in theinternal mass storage (1147). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1141), GPU (1142), massstorage (1147), ROM (1145), RAM (1146), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of embodiments, or they can be of the kind well known andavailable to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1100), and specifically the core (1140) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1140) that are of non-transitorynature, such as core-internal mass storage (1147) or ROM (1145). Thesoftware implementing various embodiments can be stored in such devicesand executed by core (1140). A computer-readable medium can include oneor more memory devices or chips, according to particular needs. Thesoftware can cause the core (1140) and specifically the processorstherein (including CPU, GPU, FPGA, and the like) to execute particularprocesses or particular parts of particular processes described herein,including defining data structures stored in RAM (1146) and modifyingsuch data structures according to the processes defined by the software.In addition or as an alternative, the computer system can providefunctionality as a result of logic hardwired or otherwise embodied in acircuit (for example: accelerator (1144)), which can operate in place ofor together with software to execute particular processes or particularparts of particular processes described herein. Reference to softwarecan encompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. Embodiments encompass anysuitable combination of hardware and software.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

The invention claimed is:
 1. A method of controlling intra predictionfor decoding of a video sequence, the method being performed by at leastone processor, and the method comprising: based on a reference lineindex signaling a first reference line nearest to a coding unit, among aplurality of reference lines adjacent to the coding unit, applying intrasmoothing on one or more first reference lines comprising the firstreference line, among the plurality of reference lines, while preventingapplication of the intra smoothing on one or more second reference linesother than the one or more first reference lines, among the plurality ofreference lines; and based on the intra smoothing being applied on theone or more first reference lines, applying intra prediction on thecoding unit.
 2. The method of claim 1, wherein the one or more firstreference lines further comprises a second reference line among theplurality of reference lines.
 3. The method of claim 1, wherein the oneor more first reference lines further comprises other reference linesother than the first reference line, among the plurality of referencelines, except for a single reference line among the plurality ofreference lines.
 4. The method of claim 1, further comprisingdetermining whether an intra prediction angle corresponding to an intraprediction mode for decoding the video sequence is greater than apredetermined angle corresponding to a diagonal direction of the codingunit, wherein the preventing the application of the intra smoothingcomprises, based on the intra prediction angle being determined to begreater than the predetermined angle, preventing the application of theintra smoothing on other reference lines other than the first referenceline, among the plurality of reference lines.
 5. The method of claim 1,further comprising, based on the intra prediction being applied on thecoding unit, applying a position-dependent intra prediction combination(PDPC) on one or more third reference lines comprising the firstreference line, among the plurality of reference lines, while preventingapplication of the PDPC on one or more fourth reference lines other thanthe one or more third reference lines, among the plurality of referencelines.
 6. The method of claim 5, wherein the one or more third referencelines further comprises a second reference line among the plurality ofreference lines.
 7. The method of claim 5, wherein the one or more thirdreference lines further comprises other reference lines other than thefirst reference line, among the plurality of reference lines, except fora single reference line among the plurality of reference lines.
 8. Themethod of claim 5, further comprising determining whether an intraprediction angle corresponding to an intra prediction mode for decodingthe video sequence is greater than a predetermined angle correspondingto a diagonal direction of the coding unit, wherein the preventing theapplication of the PDPC comprises, based on the intra prediction anglebeing determined to be greater than the predetermined angle, preventingthe application of the PDPC on other reference lines other than thefirst reference line, among the plurality of reference lines.
 9. Themethod of claim 1, wherein the one or more first reference lines furthercomprises at least one of other reference lines other than the firstreference line, among the plurality of reference lines, based on anintra prediction mode for decoding the video sequence and an index ofthe at least one of the other reference lines.
 10. The method of claim1, further comprising: based on the reference line index signaling asecond reference line among the plurality of reference lines,determining a range of index values of a plurality of intra predictionmodes adjacent to a horizontal direction of the coding unit, based on anindex of the second reference line; determining whether a current indexvalue of a current intra prediction mode for decoding the video sequenceis within the range of index values; and based on the current indexvalue being determined to be in the range of index values, preventingthe application of the intra smoothing on the second reference line. 11.The method of claim 1, further comprising: based on the reference lineindex signaling a second reference line among the plurality of referencelines, determining a range of index values corresponding to a pluralityof intra prediction modes adjacent to a vertical direction of the codingunit, based on an index of the second reference line; determiningwhether a current index value of a current intra prediction mode fordecoding the video sequence is within the range of index values; andbased on the current index value being determined to be in the range ofindex values, preventing the application of the intra smoothing on thesecond reference line.
 12. An apparatus for controlling intra predictionfor decoding of a video sequence, the apparatus comprising: at least onememory configured to store computer program code; and at least oneprocessor configured to access the at least one memory and operateaccording to the computer program code, the computer program codecomprising: first applying code configured to cause the at least oneprocessor to, based on a reference line index signaling a firstreference line nearest to a coding unit, among a plurality of referencelines adjacent to the coding unit, apply intra smoothing on one or morefirst reference lines comprising the first reference line, among theplurality of reference lines, while preventing application of the intrasmoothing on one or more second reference lines other than the one ormore first reference lines, among the plurality of reference lines; andsecond applying code configured to cause the at least one processor to,based on the intra smoothing being applied on the one or more firstreference lines, apply intra prediction on the coding unit.
 13. Theapparatus of claim 12, wherein the one or more first reference linesfurther comprises a second reference line among the plurality ofreference lines.
 14. The apparatus of claim 12, wherein the one or morefirst reference lines further comprises other reference lines other thanthe first reference line, among the plurality of reference lines, exceptfor a single reference line among the plurality of reference lines. 15.The apparatus of claim 12, wherein the first applying code is furtherconfigured to cause the at least one processor to: determine whether anintra prediction angle corresponding to an intra prediction mode fordecoding the video sequence is greater than a predetermined anglecorresponding to a diagonal direction of the coding unit; and based onthe intra prediction angle being determined to be greater than thepredetermined angle, prevent the application of the intra smoothing onother reference lines other than the first reference line, among theplurality of reference lines.
 16. The apparatus of claim 12, wherein thecomputer program code further comprises third applying code configuredto cause the at least one processor to, based on the intra predictionbeing applied on the coding unit, apply a position-dependent intraprediction combination (PDPC) on one or more third reference linescomprising the first reference line, among the plurality of referencelines, while preventing application of the PDPC on one or more fourthreference lines other than the one or more third reference lines, amongthe plurality of reference lines.
 17. The apparatus of claim 16, whereinthe one or more third reference lines further comprises a secondreference line among the plurality of reference lines.
 18. The apparatusof claim 16, wherein the one or more third reference lines furthercomprises other reference lines other than the first reference line,among the plurality of reference lines, except for a single referenceline among the plurality of reference lines.
 19. The apparatus of claim16, wherein the third applying code is further configured to cause theat least one processor to: determine whether an intra prediction anglecorresponding to an intra prediction mode for decoding the videosequence is greater than a predetermined angle corresponding to adiagonal direction of the coding unit; and based on the intra predictionangle being determined to be greater than the predetermined angle,prevent the application of the PDPC on other reference lines other thanthe first reference line, among the plurality of reference lines.
 20. Anon-transitory computer-readable storage medium storing instructionsthat cause a processor to: based on a reference line index signaling afirst reference line nearest to a coding unit, among a plurality ofreference lines adjacent to the coding unit, apply intra smoothing onone or more first reference lines comprising the first reference line,among the plurality of reference lines, while preventing application ofthe intra smoothing on one or more second reference lines other than theone or more first reference lines, among the plurality of referencelines; and based on the intra smoothing being applied on the one or morefirst reference lines, apply intra prediction on the coding unit.